(1) Field of the Invention
The present invention relates to the field of systems for heating the cabin of a vehicle. The present invention relates to a system for heating the cabin of a vehicle provided with an annular heat exchanger situated around an exhaust pipe, and it also relates to such an annular heat exchanger positioned around an exhaust pipe. The invention is particularly applicable to heating the cabin of a rotary-wing aircraft.
(2) Description of Related Art
It is known that a fraction of the heat generated by at least one engine of a vehicle can be used to heat the cabin of the vehicle.
For example, in automobiles, the majority of the engines in current use are liquid-cooled. The heat transmitted by the engine to the cooling liquid can then be used through a heat exchanger to heat the air taken into the cabin of the vehicle.
However, that technique is rarely used in aviation. Aircraft are often powered by turbine engines that do not have cooling systems using cooling liquid. Other techniques for heating the cabin have therefore been developed for aircraft.
The cabins of airplanes that fly at high altitude are generally pressurized. The difference in pressure between the outside air and the inside air can then be used to drive air circulation, e.g. via a turbine driven by said difference in pressure. That air can then be heated or cooled to regulate the temperature of the cabin of such an airplane.
However, such a solution is not applicable to aircraft having cabins that are not pressurized, such as the majority of rotary-wing aircraft. In such an aircraft, it is possible to use the compressed air for feeding the combustion chamber of the engine of the aircraft, and more particularly of a turbine engine. That compressed air has a temperature that is generally about 350 degrees Celsius (350° C.) at the compressor outlet. It is then possible to tap a fraction of that compressed air and to mix it with the outside air in order to heat the cabin of the aircraft. In addition, using that compressed air also procures excellent circulation for the heated air mixture inside the cabin of the aircraft.
That technique is the technique that is currently in the most widespread use in rotary-wing aircraft such as helicopters, but, unfortunately, it suffers from drawbacks.
Firstly, that technique is recognized as being a source of noise for the cabin of the aircraft, that noise mainly being due to the whistling generated by the compressed air expanding on being taken into the cabin.
In addition, that compressed air exits from the compressor at a high temperature, of about 350° C., as indicated above, and, in general, flows through ducts along the fuselage of the aircraft. Any rupturing of those ducts can then have serious consequences. Particularly severe safety measures are taken for such ducts and they are equipped with leak detection alarms.
Finally, tapping compressed air at the outlet of the compressor of an engine generates loss of efficiency for the engine and therefore a reduction in its power.
The exhaust gas from the engine of such an aircraft is removed at a very high temperature, of the order of 700° C., and can therefore also be a source of heat for heating the cabin of the aircraft.
For example, known Document U.S. Pat. No. 2,341,549 describes a system for heating the cabin of a vehicle. That system has a first pipe through which the cabin air circulates and which passes through the exhaust pipe of a turbine engine of that vehicle. However, in order to remove the risk of exhaust gas propagating into the cabin in the event of the first pipe leaking, that first pipe is situated inside an intermediate pipe through which a fluid flows, that intermediate pipe being in contact with the exhaust gas. The exhaust gas heats the fluid in the intermediate pipe, which fluid then heats the air for the cabin of the vehicle.
In addition, Document U.S. Pat. No. 3,971,511 describes a system for heating the cabin of an aircraft. An air-heating chamber is positioned at the engine of that aircraft and surrounds portions of the exhaust pipes of that engine. The air inside that heating chamber is then heated via the exhaust pipes through which the exhaust gas from the engine flows, and it is then guided towards the cabin via dedicated tubular pipes, while optionally also being mixed with air from the outside. The cabin can thus be heated by that air.
In addition, Document U.S. Pat. No. 4,490,989 discloses an air-conditioning and heating system for the cabin of a helicopter. The cabin is heated by the air circulating along a pipe passing through an air-heating chamber positioned at the engine of that aircraft and surrounding portions of the exhaust pipes of that engine.
Document U.S. Pat. No. 6,568,203 describes a system of supplying temperature-controlled air for an aircraft. That system makes it possible to cool compressed air by passing cooling air through a heat exchanger.
Document U.S. Pat. No. 4,319,630 is also known. That document describes a heat exchanger comprising two sets of U-shaped tubes. The U-shaped tubes of each set point in opposite directions and the two sets face each other. Two fluids flow independently in that heat exchanger, a respective one of the fluids flowing through the tubes of each set. Thus, heat exchange can take place between those two fluids.
Finally, Document EP 0 131 508 describes a column heat exchanger having vertical tubes. Heat exchange is then possible between a first fluid flowing around the vertical tubes and a second fluid flowing inside those tubes. That heat exchanger also has an auxiliary cooling device formed by one or more sheaths surrounding portions of the vertical tubes, it being possible for the first fluid to flow around those sheaths.
However, such heating systems use a heat exchanger for causing the air injected into the cabin to be heated by means of the exhaust gas. Such a heat exchanger is generally of non-negligible weight and volume, which can degrade the performance of the aircraft.
In addition, the exhaust gas exits from the combustion chamber of the engine at high speed, and it can suffer considerable head loss while flowing through the heat exchanger, which then gives rise to loss of power of the engine.